Jjoluiiiuj wm



g- 2" 1932- E. A. SPERRY Re. 18,555

FISSURE DETECTOR FOR METALS Original Fil ed Aug. 10. 1928 s Sheets-Sheet 1 INVENTOR II 23' ELMER. A.SPERRY, J

Exec

% 6 B EDWARD G.SPERRY, m.- 7-

ATTORNEY Aug. 2, 1932. E. A. SPERRY 18,555

FISSURE DETECTOR FOR METALS Original Filed Aug. 10, 1928 3 Sheets-Sheet 2 M W412 114' v 6 14 51 111 115 115 15' JIIIIII n $7 9' ll 4 .9 I b E LME Q TS SER Diclhilb WA RD .SPER Exzunen 34%) ATTORNEY v Aug., 2, 1932. E. A. SPERRY FISSURE DETECTpR FOR METALS v3 Sheets-Sheet 3 Original Filed Aug. 10, 1928 INVENTOR LMER A lan G pronouncedly by other variations in the lphyfield su rroun UNITED STATE-S PA-TENT" oratora, army, nncnasm), LATE or nnooxmm, m roux, u army rnonuc'rs,

' me, or noon-n1, m roux, Mammal: v

n'ssonn 'nmncron r03 mam membranous, dated augu'at 2s, les ian-m mi. seam, fled Least 10. me. Application? reissue fled larch ll, Seth! Io.

This invention relatesto means for detectin inequalities, flaws, fissures, slag or 'other im tlusion's and abnormal conditions generally in metal sheets, wires, bars, rails or the like. These faultsmay either be hidden or at or neai the surface and possible of discernment. The invention has also especial adaption to detection of flaws or fissures 1n railway rails either before or after being laid on the track, since such-fissures frequently cause breakage'of rails, derailment, and consequent disaster. A method of detecting such fissures has been heretofore ropose wherein the magnetic properties oft e rail is utilized. According to this prior method the railis placed in' a strong magnetic field which is moved relatively to the rail, andmeans are employed to detect variations in the field produced by the varying permeability of the rail from the point to point. The theory was that a hidden fissure would cause a variation in the number of lines of force passin through the object which could be detected the resultant variation in the ding the object, but the method failed because variations in such field were produced not only byfissures but often more sicalcharact -istics of the rail, such as ard spots, soft'spots, hammer blows, gag marks, etc. Such a method, therefore, failed of its urpose, for itwas impossible to distinguish between fissure indications and those due to other causes which do not seriously weaken the rail. This method also is obviously not adapted for testin magnetic meta l,.suc as iron or steel for it is dependentupon the magnetic permeability of the material. I

According to this invention, however, instead of passing magnetic lines of force through the body to be tested, there is passed a direct electric current of suitable strength as set forth in Patent No.- 1,804,380, issued -May 5, 1931, and there are detected variations in the uniformity of the path of the flow of the current through the rail which are produced when the currentflows around va flaw or fissure, the current flow, especially'if direct current is employed, being: comparatively I ter 'method there is .as a wire or coil of wire, which is resgoneld any metal but onlya current through the con nary railroad rail, such a change in the path 'una -fl'ectedby hard spots and the like. The

present method, therefore, is similar to the prior methods disclosed in the above mentioned patent, .but is distinguished therefrom in that according to the present method there is, avoided the necessity of using the detector contacts on the Irail. Afterre "ated experiments and actual tests on rel ways, it was found that good contact of the detector brushes of the rail on laid track was difiicult to obtain uniformly,,' some rails having a.

tough insulating coating-thereon which inered seriously with the high precision necessar 'in the accurate detection ofthe fis sures. ccording to the present invention, the necessity for employi detector brushes to pick upthe potential rop variations is dispersed with and instead of such contact laced nearthe rail through which current is ing passed, a member, such sive to variations in the ma etic, surrounding the conductor cause by the pas sage of current therethrough. Said member may be connected directly or through an amplifying system to the indicator or re Garden As. such coil and conductor are moved relatively, the coil will cut'the lines of force surrounding the conductor produced by the current flowing therethrou h and hence, a small electro-motive force be induced in the coil. This will always have a more orless alternating characteristic,

whether the primary current is alternating or D. C. The wire or coil is placed so that the wires thereof extend generally parallel to the direction of the flowof current in the conductor so that the magnetic lines of force pass through the coil or loop. As long as the field around the conductor is uniform, the How o'fthe current induced in the coil will be uniform, but an variations in the field will immediately in uce a variation in the said electromotive force in the coil which can be detected. Provided the rate of currentflow is constant and the relative speed constant the only condition that can produce a varia: tion in the field is a chan uctor.v u an ordiin the ath of the r can only be produced by a flaw or a rail joint,

Fig. 2 is a plan view of the test sled or slide which rests on the rail under the car, showing the revolving armatures used as the detector coils in this form of the invention.

in a section ofthe rail head.

Fig 4 is a wiring diagram showing the simplest form of the invention.

Fig. 5 is a second diagram showing the 5 use of compensating detector coils instead of p" a single wire with ear phones as indicators.

Fig. 6 is a diagram showing one method of eliminating the effects of rail joints on the indicating means.

Fig. 7 is a dia rammatic view of the preferred form of etector coil.

Fig. 8 is a diagram showing the detector coils connected to an amplifying system.

Fig. 9 is a diagrammatic p an view showing one form of recorder or indicator which ma be used with this invention. I

lflis a side view, partlyin diagram- 'Zmatic form, of the invention as applied to "'3 testing of wire in a rolling mill. 7 to, Fig, 11 is an end eleyation of one of the main supply brushes.

Fig. 12 is an end elevation of-the apparatus looking in the direction of the arrow in Fig.

Fig. 13 is a. detail of the onegroup of main tion.

Referring first to Fig. 4 and Fig. 5, if a current is assed through the bar 1 from gen- M erator (5 and the bar possesses no'hidden flaws or fissures, the current will flow uniformly therethrough and, therefore, a uniform ma etic field will surround the bar. how; r, thereis a fissure or blowhole at say point? in the bar, which lies near the top,

' the mtin portion of the current will pass under the fissure as shown by the arrow 3. This will of course, produce a changein'the magnetic field surrounding the bar at that '4? point, weakening the field above the bar. If then the .wire 4 of Fig. 4 or the coil or coils.

6 and 7 of Fig. 5 are movedrelative to the bar near the surface thereof, the E. M. F. or current induced in the same will be varied as point 2 is passed over, which variation may Fig. 3 is an end elevation "of the sled showsupply brushes, parts being shown in sec be utilized to give an indication of the flaw. This variation may be amplified in any suitable manncr at 4, such as by thermionic tubes (see Fig. 8) to actuate a recorder (Fig. 9) or indicator 5, or the coils may be connected 7 to ear phones 5, which act both as an amplifier and detector. Preferably the coil is provided with a core 6, of material of high magnetic permeability so that the maximum number of lines of force will traverse the coil. Experience up to the present points to the remarkable alloy known as permalloy giving the best results for this purpose. This alloyalso becomes saturated at low mangetic densities and when laminated shows low hysteresis losses. Also, it is preferable to employ a second coil 7, cross connected withthe coil 6, so as to balance out the effect of variations in the physical speed relatively between the coil and conductor and also any variations in voltage in the main supply current through the same. In other words, if the amount of current flowing through the conductor or the speed of travel varies materially, a change in E. M; F. would be simultaneously generated in each coil, but since the two coils'are opposed, this would balanceout so that no indication would reach the amplifier, receiver or indicator.

A preferred form of the invention in which an amplifying system is unnecessary is shown in Figs. 1 and 2, this form being especially adapted for testing rails on a laid track. The apparatus is mounted on a test car 8. Under the car and over each rail is suspended a sled or housing 10, which, in operation, rests on or near the rail. Said sled is shown provided with curved sides and ends and has housed therein a pair of armatures 11 and 12, which are normally revolved at good-speed by means such as a motor 13 in the car body,

connected by flexible shaft 14, to a pinion 15, which meshes with a gear 16 on the common shaft 17 of the two armatures. That portion of the shaft 17' connecting the two armatures, at least, should be of non-magnetic material. Each armature as shown is provided with a laminated wound core and also preferably unwound pole shoes'13'of high permeability, so as to direct a maximum number of lines of force through the armature. The commutator and'brush housings 18 are also preferably made of non-magnetic material.

As in the case of the two coils 6 and 7, the

armatures. are cross-connected so'that current will only pass through the system when the E. M. F. of one armature varies with respectto the E. M. F. of the other armature, thus cancelling out the effect of variations in the supply voltage, speed, etc. By' revolving the armatures at high speed an indication of a flaw may be obtainedvwithout other amplifying means, for therevolving armature cuts the lines of force rapidly ing an auxilia i il I sistance of t encountered the resistance is'suflicient to indicator.

' the wiring connections to be shown.

purpose ofthetwo pairs is .to balance out and produces a suflicient current to properly aetuate the relay coils or the indicator devices. v

The sled may be raised and. lowered by meansof the bell crank lever 27 which is connected to the bar 28, from which the sled pro r is supported on rods 29, coil sprin 30 in shown to press the sled against t e track, maintaining the armatures a constant distance above the rail. Bell crank lever-27 is shown as operated by link 31 connected to hand lever32. A canopy or top 33 is shown as overlying the body 01 the sled (see Fig.3) so as to kee out rain and foreign matter and also shiel the set from stray magnetic or electric fields. The sled is rovided with extending ends 20, each of w ich su rts the main suppl brushes 21, 22.

Rb of said ends 1's,a so shown as carrybrush 23 which contacts with the rail. is to temporarily paralyze the indicator when a rail joint is assed over, so that the rail 'oints willnot s confused with the fissures. n this system (Fig. 6) the two brushes 23, 23' are shown as connected to a relay'magnet 24, which, when excited attracts armature 25 and opens switch 26. said switch is in circuit with the ear phones or other indicator, so that at this timethe circuit to the same is o 11. When both brushes 23 and 23' are on e same rail, little or no current will flow through rela 24 on account of the low rerail, but'when a rail- 'oint is cause enoug current to flow through the relay in ct to attract the armature 25 and thus brea the circuit to the indicator. Said relay may also 0 rate any suitable rail counting device 11 as shown in said prior Patent No. 1,804,380.

Fi 7 shows one form of detector coil in' whic the coil is wound around a core 34 of hi rmeabilit ,connecting end pieces or- 'la rall ged actuated only the rail.

y enlar extensions 35.

As. stated, the coils may be connected with a thermionic amplifying system similar to that emplo ed in said' rio'r Patent No. 1,804,380. shown in ig. 8 two pairs of cross connected coils 6 and 7, 6 and 7' are connected to the gridn140' of the first tube 140 and afnumber of amplifying employed, to o rate relays for actuatingzz an coils are shown turned fromltheir operative position in for the purpose of, permitt li llilg' e through Fig. 5 only flaws and the relative size of the flaw indicated. The whole arran ment is, of course, varied to suit the con tions and also the e purpose of said brush 23- i of the rail 'oint counter 117.

character of. the primary current and secondary indications.

The intermediate amplifying tubes I tube 104 has a plate thereon connected to a lurality of relays 105, 106, 107 for controlmg the indicator or recorder pro er, which is preferably in the form of a p uralit of markin cord on a continuousl advanced strip of paper P (see Fig. 9). 1% this form of the invention a separate rail 'oint relay 108 is employed which controls 1: e rail 'omt marking pen. Said relay is connected with preferably a separate set of amplif 'ng tubes 109-110, which have a less amplit tubes 100101. The grid 109 of tube 109 is shown as connected in parallel with the of tube 101 of the main group, and the p ate 110'- of the last tube 110 is connected to the rail joint rela 108. The respective pen relay contacts are s own as connected to the respec- 'tive pen magnets 111, 112, 113, while the rail joint relay is connected to the rail joint mark- 1In this figure there are three flow magnets 9 112, and 113 and one joint magnet 114 for the left hand rail and three flaw magnets 111', 112' and 113. and a joint magnet for theright hand rail, but'only one joint pen 114'. Coll inFig. 8 isthe operating coil As state above the 'se araterelays-are wound .or adgicsted for .di erent degrees of sensitivity. la magnet 108 in this instance is relative y insensitive so that it is by rail joints or other gaps in The other relays are pro essively more sensitive. For a small flaw on y one relay 105, for instance, is desi ed to be operated, fora large flaw two rel and for a serious flaw three relays 105, 106

and 107. Thus theindications on the chart show at a the relative size of the, fissureaswe asits presence. I

Referring to Fi 9, the rail joints in the left hang ,rail are own at a b,c'and in the right rail at d'and-e, because the n 116 of vcoils 114 and 115 is only actuat such. A very small to is shown in the left hand rail at f, because'only'the supersensitive relay 105 for n magnet 111 1s actuated by such a sum] flaw. A larger flaw is indicated-at g; in the left hand rail and a vely serious flaw t h in the left hand rail an at It in the 'ght hand .rail. It will be understood that the chart P of Fig. 9 is adid i g pen magnets 111, 112, 113 whic reing coefiicient than,

ays 105 and 106,

- mined extent. It is preferable to shown in the aforesaid prior Patent No.

It is obvious that the system is equally well adapted for testing any metallic wire or rod and in Figs. 10, 11 and 12 there is shown the preferred form of the invention for testing wire as it passes through the rolling mills.

The wire is shown at and is represented as moving rapidly in the direction of the arrow between the rollers '51, 52. Current is suplied to the wire by the main brushes 53, 54. tween said brushes are placed a pair of spaced detector coils 55, 56 which, in this instance, surround the wire to some predeterlace beyond the brushes 54 a second pair 9 detector coils 55', 56, for a purpose hereinafter described. All of said coils arepreferably split or open at one side together with the permalloy centers 57 and are mounted on hinged frames 58, 59 so that they may be opened as shown in dotted lines in Fig. 12, the two frames being hinged at the point 60. Frames 58 and 59 are each provided with ears 61, 62 extending beyond the pivot and connected to a spring 63 which normally tends to pull the ears together as shown in dotted lines in Fig. 12 and thus open the coils. A pair of pivoted links 65, 65 are shown as hinged to cars 61, 62, forming a pantograph. The outer end of the panto raph is shown as slidable 1n 8. slot 67' in brac ltet 67 and is normally held forwardly, as shown in Fig. 12 by trip 68, secured to a shaft 69'. When said trip 68 is revolved upwardly as' shown in dotted lines, the spring immediately opens the coils as shown in Fig. 12, thus releasing the wire and placing the coils where they will not be harmed by the loose end of the wire as it flies through the apparatus. L

. Resting on the wire at the right side of the apparatus is showna wheel 70 which is revolved by the passage of the wire thereunder.

Said wheel is shown as driving through suitable bevel gearin 71, a shaft 72 which operates through exible shaft 72', a linear measuring device 73 so that if a flaw is encountered the section of wire it lies in may be readily located. Said shaft is also shown as operating a speed indicator74. The wheel 70 is journalled on a. bell crank lever 75 pivoted on shaft 76. The upwardly extending arm 77 of the bell crank lever normally makes contact with a switch. 7 8, When, therefore, the wire passes from under the wheel 70 it drops down, moving arm 77 out from engagement with switch 78. Switch 78 is in the main circuit of the supply brushes so that means are thus provided for opening the main supply current when the end of the wire is reached, thus prevent'ng severe sparking at the main supply brushes.

It is preferable to connect the speed indicator 7 4 with a resistance or other means for varying the amount of supply current. It is found advantageous to send as much current as possible through the wire and this amount may, of course, be increased with the speed of the wire, since at h'gh speed the wire will not have time to heat up and may carry many times the current it could carryif at rest. Means are, therefore, provided for increasing the current with the speed or, stat-ed another way, for decreasing the current as the speed decreases, thus providing for maximum operatin efliciency under all conditions w'thout the anger of overheating the wire. To this end the speed indicator has been shown as operating a rheostat or variable resistance 40, the movable arm 41. in the rheostat being connected to or actuated by the speed indicator so when the speed is low a much'less current s sent through the wire. than when the speed is great.

Preferably also means are provided to move the main brushes out of the path of the free end of the wire, when the end of the wire is reached as well as the detector coils. For this purpose the main supply brushes are shown as mounted for slidin in four radial Slots 80 in a supporting frame 81 so that the brushes may be moved into or out of contact with the wire 50 (Fig. 11). Each brush has a pin 82 thereon wh ch connects to the slot adjacent the brush and bears on one portion of a four-part cam 83. When the cam is revolved counter-clockwise, i. e. in the direc tion of the arrow in Fig. 11, it will readily be seen that all four brushes will be wi-th-. drawn from contact with-the wire 50. The brushes are normally held against the wire by a continuous spr'ng band 84 (seeFig. 13). The brushes are also preferably placed at a slightly different angle to the wire as shown.

' Said cam 83 is preferably revolved to withdraw the brushes by the dropping of the roller 70 as it reaches the end of the wire, which operation also performs the other functions described above. As shown, a link 85 is pivoted to the cam which is. connected to the lever 86 pivoted at 87. The outer end of said cam is in turn connected to a link 88 which is pivoted'to bell crank lever 89. Said lever in turn is shown as secured to shaft 89' which is operated from shaft 76 through bevel gears 7 6. Atits lower end, lever 89 also operates the hell crank lever 68 by a pin slot connection 90 so that the main supply brushes are withdrawn at the same time that the split coils are open to prevent damage to the apparatus.

The second pair of'split coils 55, 56"may be constructed and operated in the same manner as the main test coils. These coils, however, it should be noted, are placed around the wire at a point where no current is passing therethrough. Hence, whenever current rior construction has a material efiect on the produced by the magnetism ma etic field of t e wire itsel but has little or no effect on the flow of current therethrough.

accordance with the provisions of the patent statutes, there is herein described the principle and operation of the invention, to-

gether with the apparatus which is now considered to represent the best embodiment thereof, but it is understood that the ap aratus shown is only illustrative and that t e invention can be carried out by other means. Also, while it is designed to use the various features and elements in the combination and relations described, some of these may be altered and othersomitted without interfering with the more general results outlined, andtheinvention extends to such use.

Having. described the invention, what is claimed and desired to be secured by Letters ,Patentis:

i 11. The method of detecting'flaws within electrical conductors, which consists in passing direct current therethrough, cutting the lines of force surrounding the conductor by movin said conductor and two other conductors re atively, said last two conductors being out of contact with said first conductor, and comparing the E. M. F.s induced in said last two conductors.

2. The method of detecting flaws within 0 electrical conductors, which consists in passing direct current therethrough, cutting the lines of force surrounding the conductor by moving said conductor and two other conductors relatively, said last two conductors being out of contact with said first conductor and so arranged as to pass in succession over said first conductor substantially parallel to the direction of flow of current, and comparing the E. M. F.s induced in said last two I conductors.

3. The method of detecting flaws within electrical conductors, which consists in passing direct current therethrough, cutting the lines of force surrounding the conductor by moving said conductor and two other conductors relatively, said last two conductors being out of contact with said first conductor 1 and arranged in tandem substantially parallel to the direction of flow of current, and op 'ng against each other the E. M. F.s in uced in said last two conductors.-

A 4. The. method of detecting flaws within electrical conductors, which consists in passing current therethrough, cutting the lines of forcesurrounding the conductor by moving said conductor and two other conductors rela constant distance between the first conductor.

and said last two conductors.

5. Apparatus for detecting flaws within electrical conductors comprising, in combination, means for passing a direct current through the conductor to be tested, a pair of ogposed conductors out of contact with but a acent to said first conductor and movable relative to said first conductor, and means for indicating the E. M. pair oficonductors.

6. Apparatus for detecting flaws within electrical conductors comprisin in combination, means for passing a meet current through the conductor to be tested, a air ofogposed conductors out of contact with but a acent to said first conductor and movable relative to said first conductor, said pair of conductors being arranged to pass over said first conductor successivel substantially parallel to the direction of fl means for indicating the E. M. F.s induced in said pair of conductors.

7. Apparatus for detecting flaws within electrical conductors comprising, in combi- F.s induced insaid ow of current, and

nation, means for passingea'direct current said pair of conductors.

through the conductor to tested, a 'r of ogposed conductors out of contact with vbut a acent to said first conductor and movable relative to said first conductor, said pair of conductors being arranged to pass over said first conductor successively substantially parallel to the direction of flow of current,

and means for indicating the difierential E, M. F.s induced in said pair of conductors.

8. Ap aratus for detecting flaws within electrical tion, means for passing a meet current through the conductor to be tested, a pair of opposed conductors out of contact with but adjacent to said first conductor and movable relative to said first conductor, said pair of conductors being arranged in tandem along' conductors comprisin in combinathrough the conductor to be tested, a pair of opposed inductance coils out of contact with but adjacent tosaid conductor and movable relative thereto, said coils being arranged in tandem to pass oversaid first conductor suc- Ill cessively substantially parallel to the direction of flow of currents, and means, for indieating the differential E. M. F.s induced in said coils. 3

10. Apparatus for detecting flaws within electrical conductors Comprising, in combination, means for passing a current through the conductor to be tested, a pair of opposed conductors out of contact with but adjacent to said first conductor and movable relative to said first conductor, means for maintaining a constant distance between the first conduc tor and said pair of conductors, said pair of conductors being arranged to pass over said first conductor successively substantially par allel to the direction of flow of current, and means for indicating the E. M. F.s induced in said pair of conductors.

11. Apparatus for detecting inequalities in rails and the like, comprising the combination with means for passing a primary current through the conductorto be tested, of a secondary conductor movable relatively along the first conductor, means responsive to variations of current in said secondary conductor for giving the indications, and means for preventing the actuating of said responsive means by rail joints and like interruptions. v

12. Apparatus for detecting flaws in electrical conductors comprising the combination with means for passing a primary current through the conductor to be tested, of a test coil mounted adjacent said conductor, means for revolving said coil, means for also moving said coil along conductor relatively, and indicating means actuated by variations in the current generated in said coil.

13. Apparatus for detecting flaws in electrical conductors comprising the combination with means .for passing a primary current through the conductor to be tested, of a pair of opposed coils mounted adjacent said con-' ductor, means for revolving said coils, means for also moving the same along said conduc tor relatively, and indicating means actuated by variations in the resultant E. M. F. generated in said coils.

14. 'A flaw detector for rails comprising the combination with a car, of means thereon for passing a current between spaced points on the rail as said car moves along the rail, 9. palr of opposed coils, means for supporting the same in close proximity to the rail betweenthe points of current introduction thereto, and means for indicating variations in the induced E. M. F. in said coils.

15. A flaw detector for rails comprsing the combination with a car, of means thereon for passing a current between spaced points on the rail, a pair of opposed coils, means for supporting the same in close proximity to the rail between the points of current introduction thereto, means forindicating variations 1n the induced E. M. F. in said coils, and means for cutting out said indicating means 3: when a rail joint is passed over.

16. A flaw detector for rails comprising the combination with a car, of means t ereon for passing a current between spaced points on the rail as said car moves along the rail, a pair of opposed coils, means for supporting the same in close proximity to the rail between the points of current introduction thereto, means on the car for continuously revolving said coils, and means for indicating variations in the induced E. M. F. in said coils.

17 In a device for detecting flaws in electrical conductors, a source of current for energizing said conductor to establish an electromagnetic field surrounding the same, a detector unit adapted to be moved relative to said conductor, said unit comprising more than two conductively connected coils adapted to cut the lines of force of saidfield.

18. In a device for detecting flaws in electrical conductors, a source of current for energizing said conductor a detector unit adapted to be moved relative to said conductor, said unit comprising more than two conductively connected coils in balanced relation so that variations in current supply will not affect the output of said unit.

19. In a device for detecting flaws in electrical conductors, a source of current for energizing said conductor to establish an electromagnetic field surrounding the same, a detector unit adapted to be moved relative to said conductor, said unit comprising a plurality of sets of conductively connected detector goills adapted to cut the lines of force of said 3 20. In a device for detecting flaws in rails, a detector unit adapted to be moved relative to said rail, said unit comprising a pluralit of sets of detector coils, each of said coi s being arranged with its axis substantially parallel to the top surface of the rail.

' 21. In a device for detecting flaws in rails, a detector unit adapted to be moved relative vto said rail, said unit comprising a plurality of sets of detector coils, each of said coils being arranged with its axis substantially parallel to the top surface of the rail and substantially at right angles to the direction of said movement.

22. In a device for detecting flaws in electrical conductors, a source of current for energizing said conductor to establish an electromagnet c field surrounding the same, a. dotector unit adapted to be movedrelative to said conductor, said. unit comprising a. plurality of sets of conductively connected de-' tector coils adapted to cut the lines of force of said field, said sets bein so connected that the E. M. F.s generated Ey said sets on encountering a flaw are in opposition.

. Apparatus for detecting flaws within electrical conductors comprising, in combination, means including a source of current and current brushes for (passing current between Spaced polnts on sai conductor, flaw resp te" I sive means, a carriage therefor adapted tobe supported on said conductor, and means whereby said. carriage carries said, current 24. Apparatus for detecting flaws within electrical conductors comprising, in combination, means including a source of current and current brushes for passing current between spaced points on said conductor, flaw responsive means,-a carriage therefor adapted to be supported on said conductor within said points of current introduction, and

' means whereby said carriage carries said current brushes.

25. Apparatus for detecting flaws within electrical conductors such as rails and the like subject to irregularities in surface, comprising,1n combination, means for passin a current through the conductor to be teste to establish an electromagnetic field surrounding the same, inductive flaw-responsive means out of contact with but adjacent to said conductor and movable relative to said conductor .to out said lines of force,.means in sliding engagement with the conductorfor maintaining a constant distance between said conductor and said flaw-responsivemeans so that normally the latter cuts a constant number of said lines, and means for indicating variations in the E. M. F. induced in said flaw-responsive means.

26. Apparatus for detecting flaws within electrical conductors such as rails and the like subject to irregularities in surface, comprising, in combination, means for passinga current through the conductor to be tested to establish 'an electromagnetic field surrounding th same, inductive flaw-responsive "II- b means out of contact with but adjacent to said conductor and movable relative to said conductor to cut said lines of force, a sled .in engagement with the conductor for supporting said flaw-responsive means at a eon-v stant distance above said conductor so that normally said flaw-responsive means cuts a constant number of said lines, andmeans for indicating variations in the E. M. F. induced in said flaw-responsive means.

SPERRY PRODUCTS, INC Auignee 'of Elmer A. Sperry, Deceased.

' 'Iy-ELIIR A. srmn'n,

Woo Preoident. 

